The phrase "again regained" is correct and usable in written English.
It can be used when referring to something that has been recovered or obtained once more after having been lost or taken away.
Example: "After months of hard work, she finally again regained her confidence in public speaking."
Alternatives: "regained once more" or "recovered again".
Since a French-led military intervention forced the extremists from power, the N.M.L.A. has again regained its prominence in Kidal.
Despite a few app updates that added in features missing from the start, Flickr never again regained the lead, although its community still numbers in the millions.
It was only after the support of friends, teachers and my parents, that I become confident again, regained my self-esteem and could face walking past people in the corridors.
Throughout the Middle Ages, the buckle was used especially for ornamentation; but, during the second half of the 14th century, the knightly belt and buckle took on its most splendid form, and, after the early 15th century, the belt and buckle never again regained such importance.
Dunfermline again regained composure, but Alloa's more incisive play again paid dividends in first-half stoppage time.
Botvinnik again regained the title in a rematch in 1961.
And through awe, we once again regain spiritual humility.
The process is meant to finally allow MF Global customers to again regain access to their accounts.
With the decline of state churches, confessions are no longer legally established norms and can once again regain their original function of witnessing to basic convictions.
Now, after another experiment with partial water privatization — this one lasting fourteen years — residents of Berlin are once again regaining control of their water.
I have no doubt it will once again regain the public's trust both in the UK and around the world.
